How should I practice Nth Staged License Plate?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Google onsite interview problems in FastPrep.

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Nth Staged License Plate

Google● MediumINTERNONSITE INTERVIEW

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Problem statement

License plates are generated in stages for a fixed total length length. Stage k has exactly k leading uppercase letters followed by length - k digits. Stages run from k = 0 through k = length.

Within one stage, enumerate the letter prefix as a zero-padded base-26 number with A = 0, then enumerate the digit suffix as a zero-padded base-10 number. The index n is zero-based across the concatenation of all stages. Return the plate at index n.

Function

nthStagedLicensePlate(n: long, length: int) → String

Examples

Example 1

n = 0length = 5return = "00000"

The first stage starts with the all-zero five-digit plate.

Example 2

n = 99999length = 5return = "99999"

This is the last all-digit plate.

Example 3

n = 100000length = 5return = "A0000"

After 100000 digit-only plates, the one-letter stage begins.

Example 4

n = 360length = 2return = "AA"

Length two has 100 digit plates and 260 one-letter plates before the all-letter stage.

Constraints

1 <= length <= 10.
0 <= n < sum(26^k * 10^(length-k)) for 0 <= k <= length.
All intermediate counts fit in a signed 64-bit integer.